changing tires sizes alters geometry?
05-13-2011, 07:10 AM
#1
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
changing tires sizes alters geometry?
According to the chart below, changing the front tire to a 120x60 can lower the front an inch and going to a 190x55 can raise the rear by 1/2"(approx). Many have altered the front by raising forks in the triples and shimmed the rear shock to 6mm+ to increase height for quicker turn in and/or better handling. Could this be another way of accomplishing the same thing or adding to suspension changes?
I tried the 190x50, which lowers the rear by approx 3/4", and took it off after a 1000 miles and sold it.
The other thing about the 190 on a 5.5" rim is that it changes the profile making the sides steeper, however, many track riders do this and swear by it for the increased contact patch.
Since i need to replace my tires, I'm thinking about doing some experimenting and wanted to get some feedback(190x55 on 5.5" rim and 120X60 front). Any thoughts?
190/55 Mich Pure's on 5.5in Wheel - Page 2 : Suzuki GSX-R Motorcycle Forums: Gixxer.com
I tried the 190x50, which lowers the rear by approx 3/4", and took it off after a 1000 miles and sold it.
The other thing about the 190 on a 5.5" rim is that it changes the profile making the sides steeper, however, many track riders do this and swear by it for the increased contact patch.
Since i need to replace my tires, I'm thinking about doing some experimenting and wanted to get some feedback(190x55 on 5.5" rim and 120X60 front). Any thoughts?
190/55 Mich Pure's on 5.5in Wheel - Page 2 : Suzuki GSX-R Motorcycle Forums: Gixxer.com
05-13-2011, 11:12 AM
#2
Senior Member
Back Marker
Join Date: Apr 2010
Location: Prague - Czech
Posts: 219
I´d lower front in triples, it does the same and 120/60 can affect handling and grip. What I know, track riders prefers 190/55 against 190/50 for the same reason and motorcycle manufacturers as well.
05-13-2011, 12:23 PM
#3
Senior Member
Superstock
Join Date: Jul 2008
Posts: 320
Actually, going from 120/70 to 120/60 would lower front by about 1/2 inch, and going from 180/55 to 190/55 would raise the rear by about 1/4 inch, according to the chart. Only the radius of the tire would affect ride height, not the diameter.
In the same way, the 190/50 should have only lowered the rear about 0.15 inches compared to the stock 180/55, but then pinching the 190 into a 5.5" rim would make the 190/50 a little taller (not sure how much). So it probably wasn't any shorter than a 180/55 on a 5.5" rim. Did you measure a 3/4 inch difference?
And I would think a 120/60 would make the steering quicker compared to a 120/70, because it would lower the front. But that's assuming the profiles between the two tires are the same.
05-13-2011, 12:46 PM
#4
Senior Member
SuperBike
Join Date: Apr 2010
Location: Big Lick
Posts: 1,090
IMHO, learn to ride the bike to it's capability, then be worried about larger contact patches and geometry. If you can out-ride the superhawk's ability on the track, you'd want to switch to a more focused sportbike instead of tinkering with the hawk.
sorry for the diversion but I can't help myself.
sorry for the diversion but I can't help myself.
05-13-2011, 01:04 PM
#5
Senior Member
Superstock
Join Date: Jul 2007
Location: Los Angeles & Winston Salem
Posts: 433
I miss being on gixxer.com. Thats a pretty fun board. Stock most GSXR1000 come with a 190/50 rear tire. Installing a 190/55 makes for a good improvement in handling, pretty much everyone that does it will say it feels better. Not sure if running any kind of 190 width tire is a good thing on a stock Honda Superhawk rim?
let us know how you get on.
let us know how you get on.
05-13-2011, 01:20 PM
#6
Senior Member
SuperBike
Join Date: Apr 2010
Location: Big Lick
Posts: 1,090
I gotta believe it's either a)mostly in their minds; or b)they are expert riders. I just have to shake my head when "average" riders start talking about things being "better". The one thing I would accept is that they feel more confident with it. I have experienced that myself, but I know full well it's in my head, and not because I'm outriding the bikes (or tires) capabilities.
I'm just MR Negative today, aren't I. :-(
I'm just MR Negative today, aren't I. :-(
05-13-2011, 02:29 PM
#7
Out of my mind, back in 5
MotoGP
Join Date: Nov 2006
Location: Skurup, Sweden
Posts: 6,109
I gotta believe it's either a)mostly in their minds; or b)they are expert riders. I just have to shake my head when "average" riders start talking about things being "better". The one thing I would accept is that they feel more confident with it. I have experienced that myself, but I know full well it's in my head, and not because I'm outriding the bikes (or tires) capabilities.
I'm just MR Negative today, aren't I. :-(
I'm just MR Negative today, aren't I. :-(
Changing tire size does affect the geometry and the feel of the bike quite a lot... I have done back to back with a street 180/55 and a 190/50 on the stock rim, and they felt completely different...
Now, I'm not saying the average rider can identify and use one or the other to any advantage... I'm saying you can feel the change...
I'm running a completely different setup than any of you guys (6" rim, SP2 swingarm), so I'm not comparing, but 190/50 or 190/55 doesn't matter, I have to work hard to get close to the edge of the tire... I can get there, but it takes a conscious effort... On the stock swing, and 180/55 I was to the edge every time... Same with the 190/50 squeezed on there...
05-13-2011, 05:45 PM
#8
Senior Member
SuperBike
Join Date: Apr 2010
Location: Big Lick
Posts: 1,090
I hear you, and I ride at the edge of mine too. But I have never had the bike beyond the limit of both the bike and the tires. I don't even run slicks, which would provide even better grip. All I'm saying is that most of us don't have the skills to approach the limits of tire and motorcycle technology. If someone is actually that good, then I'd strongly urge the upgrade their entire mount to a bike that is more capable than the hawk. Perhaps a BMW 1000RR? :-D
05-13-2011, 05:47 PM
#9
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
First, I have no experience with this, this just made me think a little.
Actually, going from 120/70 to 120/60 would lower front by about 1/2 inch, and going from 180/55 to 190/55 would raise the rear by about 1/4 inch, according to the chart. Only the radius of the tire would affect ride height, not the diameter.
In the same way, the 190/50 should have only lowered the rear about 0.15 inches compared to the stock 180/55, but then pinching the 190 into a 5.5" rim would make the 190/50 a little taller (not sure how much). So it probably wasn't any shorter than a 180/55 on a 5.5" rim. Did you measure a 3/4 inch difference?
And I would think a 120/60 would make the steering quicker compared to a 120/70, because it would lower the front. But that's assuming the profiles between the two tires are the same.
Actually, going from 120/70 to 120/60 would lower front by about 1/2 inch, and going from 180/55 to 190/55 would raise the rear by about 1/4 inch, according to the chart. Only the radius of the tire would affect ride height, not the diameter.
In the same way, the 190/50 should have only lowered the rear about 0.15 inches compared to the stock 180/55, but then pinching the 190 into a 5.5" rim would make the 190/50 a little taller (not sure how much). So it probably wasn't any shorter than a 180/55 on a 5.5" rim. Did you measure a 3/4 inch difference?
And I would think a 120/60 would make the steering quicker compared to a 120/70, because it would lower the front. But that's assuming the profiles between the two tires are the same.
No I didn't measure the the rear 190/50, but likely as you stated. All I know is that putting the 190/50 on a 5.5" rim seems to steepen the arc and makes it difficult to eliminate chicken strips, i.e., I usually have a tiny line at the very edge on 180x55, and when i had the 190/50 and leaned the same angles, I had larger chicken strips. I don't know if i could lean more and erase the chicken strip with a 190 on a 5.5" rim because, if I recall my experiences correctly, it would slide when I tried to get over more, but that could have been the result of a poor front-rear match(Q2 front with a BTO-16 190/50 rear).
05-13-2011, 06:42 PM
#10
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
I hear you, and I ride at the edge of mine too. But I have never had the bike beyond the limit of both the bike and the tires. I don't even run slicks, which would provide even better grip. All I'm saying is that most of us don't have the skills to, approach the limits of tire and motorcycle technology. If someone is actually that good, then I'd strongly urge the upgrade their entire mount to a bike that is more capable than the hawk. Perhaps a BMW 1000RR? :-D
If you ride the edge of your tires consistently, there is a high probability that you will find that the same will happen to you. Falling off isn't a problem if you're geared, it's what you hit or what hits you that will ruin your day.
05-13-2011, 07:07 PM
#11
Senior Member
SuperBike
Join Date: Apr 2010
Location: Big Lick
Posts: 1,090
Not a dumbass. you're probably just one of those guys who is experienced enough to push the limits of the bike. I've fallen off a number of times, but in each, it was the fault of the rider and not the equipment. They were all learning experiences though. 
05-13-2011, 07:32 PM
#12
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
thanks for "not a dumbass", but I believe that most of us are, it's just that some don't realize it, which, IMO, is a more serious disability.
05-13-2011, 07:36 PM
#13
Senior Member
SuperSport
Join Date: Mar 2010
Location: Asheville, North Carolina
Posts: 949
I have over 10 GRAND in the suspension set up thru GMD computrack on the 2 RC-51s and both bikes are set up on Bridgestone 016- 120/60/17 and 190/55/17 tires- and that is the Geometry set of of these bikes- SAME as honda set up the Superhawk, change the Geometry by changing tire size- and you are in the dark... Wasting the millions that Honda invested
Every MM you move forks, or change the wieght of the spring on the rear, is "Like laying under your car and adjusting the tie-rod ends on the rack conpinion for the steering..
Even when you change tire size on a car you change the Geometry...
Every MM you move forks, or change the wieght of the spring on the rear, is "Like laying under your car and adjusting the tie-rod ends on the rack conpinion for the steering..
Even when you change tire size on a car you change the Geometry...
Last edited by 1971allchaos; 05-13-2011 at 07:39 PM.
05-13-2011, 08:37 PM
#14
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
I have over 10 GRAND in the suspension set up thru GMD computrack on the 2 RC-51s and both bikes are set up on Bridgestone 016- 120/60/17 and 190/55/17 tires- and that is the Geometry set of of these bikes- SAME as honda set up the Superhawk, change the Geometry by changing tire size- and you are in the dark... Wasting the millions that Honda invested
Every MM you move forks, or change the wieght of the spring on the rear, is "Like laying under your car and adjusting the tie-rod ends on the rack conpinion for the steering..
Even when you change tire size on a car you change the Geometry...
Every MM you move forks, or change the wieght of the spring on the rear, is "Like laying under your car and adjusting the tie-rod ends on the rack conpinion for the steering..
Even when you change tire size on a car you change the Geometry...
My geometry is fucked-up already: forks set at OEM level, and don't want to raise them for space reasons(superbike fat bars). The rear is raised by virtue of JD's f4I conversion(5 or 6mm i'd guess). If I lower the front with 120/60 1/2", and raise the rear 1/4" more with a 190x55, the bike should approximate OEM front/rear geometry, but just higher off he ground. How would a 190x55 on a 5.5" rim match up with a 120/60 in terms of leaning? That's the mystery I'm looking to resolve. Your 190x55 is on a 6" rim so it's a different story.
05-13-2011, 09:50 PM
#15
Senior Member
Back Marker
Join Date: Apr 2010
Location: Prague - Czech
Posts: 219
My geometry is fucked-up already: forks set at OEM level, and don't want to raise them for space reasons(superbike fat bars). The rear is raised by virtue of JD's f4I conversion(5 or 6mm i'd guess). If I lower the front with 120/60 1/2", and raise the rear 1/4" more with a 190x55, the bike should approximate OEM front/rear geometry, but just higher off he ground. How would a 190x55 on a 5.5" rim match up with a 120/60 in terms of leaning? That's the mystery I'm looking to resolve. Your 190x55 is on a 6" rim so it's a different story.
05-14-2011, 05:44 AM
#16
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
maybe I miss something, but if you have raised rear (and 5mm on rear shock is not 5mm on rear end), geometry is quicker. If you add higher profile on rear, geometry is affecting same way. And if you lower the front by 120/60, it does the same again. Result is quite a different geometry from stock ...
120/60 tire front and 180/55 rear. Net result: 12mm lower (front tire), and 5mm rear up (shim). Not OEM geometry, but should facilitate turn-in.
05-14-2011, 08:49 AM
#17
Senior Member
Back Marker
Join Date: Apr 2010
Location: Prague - Czech
Posts: 219
nath981: Seems to be better idea than 190/55 on rear. 12mm on front is quite a lot itself IMO. I am happy with added 5mm on rear shock and little bit shorter wheel base due to oem chain lenght and 43 sprocket but preferences are individual
Last edited by Stephan; 05-14-2011 at 08:50 AM. Reason: grammar
05-14-2011, 11:52 AM
#18
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
Chain length: that's what I did too but I have 520/15/44, I think 100 links, or whatever the max I could cut off anyway.
05-15-2011, 05:07 AM
#19
Out of my mind, back in 5
MotoGP
Join Date: Nov 2006
Location: Skurup, Sweden
Posts: 6,109
yeah. I'm getting confused with my own numbers. Not unheard of for me.haha Front forks are OEM height, rear shock is lengthened 5mm. So with the 120/60 tire, the front drops about 12mm and with the 190/55 the rear is up another 6mm plus the 5mm shock. So the net result would be front down 12mm, rear raised 11mm, no where near OEM geometry and probably too radical?
120/60 tire front and 180/55 rear. Net result: 12mm lower (front tire), and 5mm rear up (shim). Not OEM geometry, but should facilitate turn-in.
120/60 tire front and 180/55 rear. Net result: 12mm lower (front tire), and 5mm rear up (shim). Not OEM geometry, but should facilitate turn-in.
Even if you leave the rear tire a 180/55, it's still 12mm front and 15mm rear... And believe me, that's plenty... Going further, you are practically standing the bike on it's nose...
The reason is simple, whatever change you make at the shock is multiplied by the linkage and swingarm, becoming much more at the wheel...
05-15-2011, 06:54 AM
#20
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
Um... Nope, the math is still wrong... Up 6mm from the tire plus 5mm shock does not make 11mm in the rear, it makes 21mm...
Even if you leave the rear tire a 180/55, it's still 12mm front and 15mm rear... And believe me, that's plenty... Going further, you are practically standing the bike on it's nose...
The reason is simple, whatever change you make at the shock is multiplied by the linkage and swingarm, becoming much more at the wheel...
Even if you leave the rear tire a 180/55, it's still 12mm front and 15mm rear... And believe me, that's plenty... Going further, you are practically standing the bike on it's nose...
The reason is simple, whatever change you make at the shock is multiplied by the linkage and swingarm, becoming much more at the wheel...
12mm down from 120/60 is the same as raising the forks in the triples 12mm, no hocus pocus like the rear. Don't know if i like the idea of a smaller front tire esp considering some of the rough roads I run regularly. The 120/60 will likely adversely affect handling and upset the front end more under these conditions. On the plus side, it might make for more equal front-rear tire wear since it will be making more revolutions than the 120/70.
05-15-2011, 08:11 AM
#21
Out of my mind, back in 5
MotoGP
Join Date: Nov 2006
Location: Skurup, Sweden
Posts: 6,109
thanx Einstein. Apersheate the correction. No wonder i had to cheat off the asian boy to pass geometry. The reason may be simple to you, but for me it's turns into a big thick cloud which causes dizziness, so I'll just take your word for the numbers.
12mm down from 120/60 is the same as raising the forks in the triples 12mm, no hocus pocus like the rear. Don't know if i like the idea of a smaller front tire esp considering some of the rough roads I run regularly. The 120/60 will likely adversely affect handling and upset the front end more under these conditions. On the plus side, it might make for more equal front-rear tire wear since it will be making more revolutions than the 120/70.
12mm down from 120/60 is the same as raising the forks in the triples 12mm, no hocus pocus like the rear. Don't know if i like the idea of a smaller front tire esp considering some of the rough roads I run regularly. The 120/60 will likely adversely affect handling and upset the front end more under these conditions. On the plus side, it might make for more equal front-rear tire wear since it will be making more revolutions than the 120/70.
I scribbled this in paint... It's heavily simplified, and not to scale or the correct angles, but it gives you an idea of why the math works out like I say it does...
The squiggly thing in the middle, being the shock, is where you add 5mm... The swingarm sits at an angle from level, and pivots at the mount... If you push it down 5mm at the shock, the end where the wheel is, moves further than 5mm...
It's not as simple as the picture, since the shock isn't mounted rigidly to the swingarm, there is also the linkage on the bottom of the shock to take into account, making the math a bit more complex... But rule of thumb, add 1 mm at the shock and it translates to 1,5 mm at the wheel if your bike is stock...
Last edited by Tweety; 05-15-2011 at 08:15 AM.
05-15-2011, 04:35 PM
#22
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
I ain't no einstein... But how about a fog light for that cloud?
Attachment 11670
I scribbled this in paint... It's heavily simplified, and not to scale or the correct angles, but it gives you an idea of why the math works out like I say it does...
The squiggly thing in the middle, being the shock, is where you add 5mm... The swingarm sits at an angle from level, and pivots at the mount... If you push it down 5mm at the shock, the end where the wheel is, moves further than 5mm...
It's not as simple as the picture, since the shock isn't mounted rigidly to the swingarm, there is also the linkage on the bottom of the shock to take into account, making the math a bit more complex... But rule of thumb, add 1 mm at the shock and it translates to 1,5 mm at the wheel if your bike is stock...
Attachment 11670
I scribbled this in paint... It's heavily simplified, and not to scale or the correct angles, but it gives you an idea of why the math works out like I say it does...
The squiggly thing in the middle, being the shock, is where you add 5mm... The swingarm sits at an angle from level, and pivots at the mount... If you push it down 5mm at the shock, the end where the wheel is, moves further than 5mm...
It's not as simple as the picture, since the shock isn't mounted rigidly to the swingarm, there is also the linkage on the bottom of the shock to take into account, making the math a bit more complex... But rule of thumb, add 1 mm at the shock and it translates to 1,5 mm at the wheel if your bike is stock...
when you add 1mm at the shock, it translates to 1.5mm at the wheel:
5 X 1.5 = 7.5mm shock
1mm at the tire is 1 mm in terms of height(from the axle to the ground):
6 mm at the tire + 7.5mm shock= 13.5mm rear height rise. You got 21mm. Am i mistaken?
05-15-2011, 05:51 PM
#24
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
05-15-2011, 11:44 PM
#25
Out of my mind, back in 5
MotoGP
Join Date: Nov 2006
Location: Skurup, Sweden
Posts: 6,109
Nope... I gave that first reply without checking my notes... On my SP2 swing 1mm = 3mm, which is why I got those numbers... On the stocker, 1mm = 1.5mm (or 1.6, really)... So 13.5mm it is... It's still messing up the mathematics though, so it needs to be taken into account, even though the difference is less...
05-16-2011, 04:57 AM
#26
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
Nope... I gave that first reply without checking my notes... On my SP2 swing 1mm = 3mm, which is why I got those numbers... On the stocker, 1mm = 1.5mm (or 1.6, really)... So 13.5mm it is... It's still messing up the mathematics though, so it needs to be taken into account, even though the difference is less...
13.5mm rear height increment(823.5mm, approx. 32.5in seat height). If I do this, I will need to experiment with front height.
1)keep the front forks OEM height,
2)raise forks up in triples,
3)or lower forks in triples(having no clip-ons leaves plenty of space to raise the front
won't be hard, just some riding.
05-16-2011, 07:49 AM
#29
Out of my mind, back in 5
MotoGP
Join Date: Nov 2006
Location: Skurup, Sweden
Posts: 6,109
Well... One thing to take into account when relaying all this information... I seriously doubt Roger recommended anything of the sort, with reference to reworked front forks... nath's forks are stiffer than stock, meaning they ride higher than stock to begin with... So the recommendation from Roger, and anyone else should probably be in relation to stock height, not stock fork position... Ie if Jamie/Greg recommends dropping the forks 10 mm after having them re-worked, then that is the new starting point... Just FYI... Since people are throwing mm this and mm that around... It always requires you to put them in relation to something, unless you are comparing apples to apples, ie untouched stock forks...
05-16-2011, 07:51 AM
#30
Senior Member
MotoGP
Thread Starter
Join Date: Aug 2006
Location: altoona, pa
Posts: 2,934
The fact is that my shock was modified by JD, ie a F4I with a gold valve lengthened 5-6mm, and i am happy with that. I also like the increased ground clearance for some of the rough roads I run. So I need to deal with the geometry based on that.
