Optimal supermoto tire sizes for lean angle

*Moved from sportbike forum

Hey All,

A while back a racer buddy explained to me that the best combo for tire size with lean angle in mind (for supermotos) is to have the front and rear tire as close to each other in terms of size and profile as possible for best and smoothest results in learning. I tried to find more info about it but found many contradictions. Some said 150 better, some said 140. And at that, they were talking about different tire models/mfgs and combinations. I tend to believe that the thinner rear tire gets you better/quicker/smoother lean and is also lighter weight so better response. But I'd like some more opinions or some stats if you have any.

My Question: Is a setup of 120/70/17 and 140/70/17 on 4.25" rims, going to get you smoother and more stable results than a 160 or 150 rear?

My current setup is Conti Attack SM's 120/140 (1.5K miles on them and loving it) 

 

Thanks for any help!

What bike ? 120/70-17 is a normal sport front tire size , that 70 profile rear is not. Get yourself a set of Michelin Pilot Power 2ct's. 120/70 and 150/60.

What are you using the bike for? racing?

Thanks for the replies!!!

It's for a DRZ400S converted to an SM. Not racing, just being an idiot on the twisties in New England. Maybe a track day or two, but nothing serious.

I'm very happy withe the Conti Attack Sm's. Very sticky.

It came up in a conversation I was having with someone. They wanted new tires for the DRZ SM, and I suggested sticking to the SM specs to keep the bike nimble, but my "proof" was anecdotal. Wondering if anyone had more input?

From what I understand 150/60/17 rear is a trade-off to keep the profile down because the pinch from the wider tires would make the tire's profile too tall. So, people drop the profile by 10 mm to compensate on a 4.5" rim. Hence the 150/60, instead.

120/70/17 Front and 140/70/17 rear is what was recommended by a sumo racer friend for a fun and whip-able bike. He said that its more fun to have the tire close in dimensions.  I also believe it is the stock dimensions for the DRZ400SM. I just dont know why its such a fun setup. I'm essentially looking for an explanation.

My theory is that the tire contact patches are more symmetrical, front to back, and the 140 tire is lighter in weight so better response... but not sure/have no proof.

Thanks!

Your last sentence is correct. Traction is a trade off with a narrow tire , though , and the handling difference is minimal.  If you look at a 1000 sportbike , the run 120/70 and 190/50.  There's  a bigger difference there.   A wide tire on a narrow rim can not make the tire taller though.  :smirk:

Thanks for the input Joe. I thought people get the 60 height tires because that keeps the profile down. Makes sense that with the steel belts, that's probably not the case. I agree that differences are probably imperceivable to the average rider, and probably should vote with your wallet (because 140's can be super expensive) I just figured a 140 will mostly be better because it's lighter, higher profile, holds heat better, transfers the heat to the sides better, and provides just as much grip as a wider, heavier tire. Though, I'd be hard pressed to notice those benefits. Plus, I gathered that pretty much the only reason a larger tire gets better traction is because of a softer compound, that would over heat on a smaller tire.

Actually, the more research I do, the more I come to conclude that 140 for a supermoto is the optimum size, at least for the smaller/weaker ones like my DRZ.

Thanks!

You've probably already seen this, but this irish dude (or Canadian... hard to tell... lol) does a good job at explaining it better than I can :D Helped me with a lot of the more complex ideas. derp

 

I highly recommend a 160 if it will fit for track day use. The availability of tires of that size is huge, and your riding a big heavy dry, a skinny rear tire won't have much effect on the handling. I don't know a single supermoto racer that uses anything smaller than a 160. That can be a real tight fit in the swing arm too, but it doesn't matter because it's worth having the extra rubber. 

 

Edited by Max1m_x
8 minutes ago, Max1m_x said:

I highly recommend a 160 if it will fit for track day use. The availability of tires of that size is huge, and your riding a big heavy dry, a skinny rear tire won't have much effect on the handling. 

Thanks Max1m. I actually want to try that one day just for shits and giggles. So I can compare. Though I'm not sure a 160 will fit, not all of them anyway. I heard they usually rub. I have a buddy that has a DRZ SM with 150/60 rear, maybe I can jump on his bike, if I notice any difference. Only catch is that I have/am used to a GPR damper, and that changes the handling characteristics a lot. Maybe I can bug him to swap the tire one day to test it out on my bike.

Rear tire size and aspect ratio affects turn in.  larger is slower.  You can still muscle the bars.  So Cal Supermoto has a good YT vid.

On 5/26/2017 at 6:53 PM, JoeRC51 said:

 

Traction is affected by the tires profile and the second number on tire sizes is the aspect ratio, its a function of the tires width to its height. yes pro supermoto racers on 450's dont run smaller tires, but they mount the 160s on the correct size rims. When you squeeze a 160 onto a 4.25 rim the profile is altered and there is not a bigger contact patch, if the rim was correctly sized say 5'' then there would be a bigger contact patch. Bigger tire doesnt always = more contact patch. I know plenty of people who put 160s on drzs and there isnt that much of a noticeable difference in there speeds vs me running a 140/70. I myself run 140/70 on drz, although I have ran 150's. the stock rim is 4.25'... take the tire manufacturers recommendations for what tire size/rim size to use. Michelin RS are pretty good tires for the drz SM dual compound 140 and seriously soft sticky sides. On my CRF450 that im building im using slicks 125/600R16.5x3.5 and 165/625R17x5.00 fitting the rear tire requires quite a bit of modifications.

 

Edited by Stupormoto

A 160/60 can be run on a 4.25 to 5.5'' rim. There are no rears worth a crap that come in a 70 profile.

have you tried the michelin RS? or bridgestone RS 10 in 140/70? were talking a DRZ here with dot track friendly tires...

 

My apologies , I never heard of a real sport tire in a 140/70 , I didn't even see it on Michelin's site. I had to Google it to actually find one listed anywhere.

I have Conti Attack SMs in 140/70. So far I love them, but I hear they aren't that great on life. I don't do much hooligan shit just a lot of twisties in the mountains  and so far 1K mi on them and wear isn't noticeable.

yea i will try those maybe, they seem quite expensive atleast where i have found them online. and pirelli makes supercorsas in 140/70. the michelin RS seem to be the right balance between price and performance and longevity. the s20 prices were very cheap but was not dual compound in 140 rear, still the price and performancealone made them worth it.

On 5/25/2017 at 7:21 AM, Funbags said:

*Moved from sportbike forum

Hey All,

A while back a racer buddy explained to me that the best combo for tire size with lean angle in mind (for supermotos) is to have the front and rear tire as close to each other in terms of size and profile as possible for best and smoothest results in learning. I tried to find more info about it but found many contradictions. Some said 150 better, some said 140. And at that, they were talking about different tire models/mfgs and combinations. I tend to believe that the thinner rear tire gets you better/quicker/smoother lean and is also lighter weight so better response. But I'd like some more opinions or some stats if you have any.

My Question: Is a setup of 120/70/17 and 140/70/17 on 4.25" rims, going to get you smoother and more stable results than a 160 or 150 rear?

My current setup is Conti Attack SM's 120/140 (1.5K miles on them and loving it) 

 

Thanks for any help!

Sorry but I am laughing my ass off at the moment.

 

 

 Your friend is sooooooooooooooooooooooooooooooooooooooooooooooooooooo wrong.

 

 OK, if you have a narrow rear wheel (4.25 or 4.5) then a 140 or a 150 rear works. Putting  160 or up on this narrow rim makes the tire balloon which makes it slower on tip in. A 5" to 5.5" a 160 works best. Keeps the tire profile REAL. Now add a 16.5 front wheel running  420 and even quicker with the correct rear wheel size. The new 16 hoop from Alpina is even QUICKER.

 

 Front tire profile on the 16.5 and 16 looks a TON like this < where a 17 looks like ) see how the 17 front tis round vs the 16.5. lso, shortening up your front offset and rear swingarm length have a lot to do with it.

 

 Not just matching tire sizes which you cannot do LMAO

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