Hi All, I cant find much on the subject, but effectively on track im getting far too much corner exit wheel spin using dunlop kr ntec tyres. My electronics package provides slip figures and Im seeing as much as 20%, which is too high Can anyone point me to any geometry articles or methods to fix this, other than power reduction Thanks
You've asked an extremely broad question, with very little situational detail. This is right up there with other classics like "Top speed, needs improvement", "Brake distance? How to Shorten?" and "Corner speed too low, pls help". The two factors affecting wheelspin on corner exit are Applied Torque and Mechanical Grip. In order to decrease wheelspin, you need to either decrease Torque or increase Grip. Since you are trying to avoid power reduction, you won't want to decrease Torque - so you need to figure out a way to increase Grip. Suspension changes, body position changes, and tire compound/pressure tuning are going to be your ticket. Now, all that said... are you simply going off your data and seeing 20% and thinking "the %slip is too damn high"? Or is it causing you a problem while riding?
Folks in the MA paddock were dealing with this issue this weekend at VIR, from Twins Cup on up to Superbike teams. I know that doesn't help solve the issue but know that you are not alone.
This is more of a question than a statement so please correct me if I'm wrong, but doesn't increasing the swingarm angle typically improve grip when exiting corners?
You forgot to mention "whats the best oil?" However the point is made; does the OP have a problem with the data or the ride? There is always going to be wheelspin, the questions are does it hurt my laptime and can I control this? It would help if OP mentioned the bike, hp, tire size/brand/pressure, track, turn speed, riding style, their level.... even then the answer is going to be a bit less of this and a bit more of that. I would be cautious about adjusting swing arm angle, the No1 way of reducing spin is throttle control.
Lap times, just are not what they used to be. The only change has been the swingarm and its pivot height - Aprilia tell me the new swingarm is more or less the same as the old one (which I was fast on), this newer on I'm slow on. Spin seems very high since the change. The install of the new arm put the pivot at 0 position, but we've reverted it back to -3 which is where the old swingarm was and its no better. Power is approx 210 BHP . Spin should be max 15% according to Aprilia. Throttle control is good, won all my wet races over the weekend. Dry pace is 5seconds off lap record Tyres are Dunlop KR 195/65 , skill level A grader, RSV4 WSBK spec bike. But im looking for general information, such as what Saiyan66 has mentioned, does lowering the pivot increase rear grip (i certainly know it changes anti squat)
The more a bike squats in the rear, the more weight the rear wheel is carrying, so the more grip it has. Decreasing swingarm angle reduces anti-squat, which means more weight transfer to rear, and more rear grip.
Over the race weekend we had the bike at 0 pivot height, it wheelied alot and slip was high. We moved it to -3mm, it wheelied far less. So, what you're saying Badger, is that if we move the pivot lower, the more the swingarm angle reduces (makes sense) as it looks visibly flatter , which reduces anti squat (we were in the 120-125 range for anti squat at 0mm), which INCREASES rear grip? I was under the impression TOO much anti squat, which I believe is what we had, would unload the front and make me run wide, but that doesnt appear to be the case. That said, we have a very long shock length.
What range of shock lengths do you use... If you current setting is at or near your upper limit, it's an easy choice to try lowering the rear to help reduce spin.
I believe its 325 to 335mm. We use 333mm, when I had good success on the old swingarm, we had 330mm It seems that I need to reduce anti squat and potentially increase the wheelbase to flatten the squat curve. Thats going to be lowering the pivot. The bike handles really well, no complaints so I'm reluctant to change ride height.
You installed a new swingarm, moved the pivot from -3 to 0, and changed the shock length from 330 to 333? All at the same time? 3 not-small changes at the same time is not a good approach to setting up a bike. It shouldn't be surprising that the bike is acting different, nor that you went slower. I also wonder what else you changed that you aren't telling everyone. The bike doesn't "handle really well". It's spinning a ton and you are slower. You shouldn't be reluctant to change anything on a race bike, and especially not with things that haven't worked. Go do a trackday and change something each session until you find a new range that works with the new swingarm.
No. The new swingarm was installed with pivot at 0. Shock at 333 - recommened by Aprilia. It never worked well. 16/42 gearing. I ran it like this for months and months, changing rear springs and gearing without ever really improving. Old setup was different swingarm, at -3, 330mm shock. It worked well. 15/41 gearing. Over the weekend, we tried the pivot in -3mm position but I've not had enough dry time to really understand the effect of the change Handles well, meaning it enters/finishes corners nicely. Not running wide etc. I'm ok changing things, but I want to understand what pivot does and it seems that it changes anti squat without altering ride height. I've learnt to decrease anti squat, lower the pivot. To increase anti squat, raise the pivot. By punching my current numbers into a squat calc I'm around the 120% which I understand to be less than ideal. Lowering the pivot seems to be the ticket including an increase in wheel base to flatten that anti squat curve.
Sry, I wasn't entirely clear. You agreed with me. From your old to new setup, you did exactly what I said. You also changed the gearing which would move the axle ~8mm. Did you also change the chain? IIRC, shortening the pivot to axle length steepens the squat curve. Perhaps Aprilia intended you to run a longer chain (+20mm for axle position, -8mm for gearing change) with their gearing recommendation (and the rest of their setup). IMO, you should return the bike to your settings, but with the new swingarm. Then try Aprilia's recommendations one at a time to see what each does. I think you'll learn more and learn it faster this way.
Thanks, with my current gearing the wheelbase is quite short and therefore the anti squat curve not overly flat. I'm going to revert also to my gearing, which removes 1 link from the chain (56links on 15/41, the good setup) vs 57 links on 16/42 (the bad setup, which actually gears the bike too tall for the circuit anyway) and check my wheelbase. Already it appears to add more wheelbase so that is indeed a good thing! I'll do as you suggest and report back, including changing my shock back to the good setting (330mm)
How much does sprocket gearing effect wheel spin? If geared to low (for example -1 front and +3 rear) wouldnt the added torque increase allowing the wheel to break loose. Did you play with tire pressure in the rear maybe drop 1 psi and see if that helped?
Something to consider: your leverage ratio may be a little off, shock length is quite long yet the arm is set flat. Your initial part of your linkage now softer. More spring preload will alleviate, but you will then lose a little more edge grip. Something i would be looking to do would be to shorten shock and raise the arm in the chassis Looking at the pics i see a thomas pappy water mark and looks to be at eastern creek. What covers are you struggling the most with? Ive done few laps of eastern creek myself, it may help if I can visualise what corners at what point your having trouble with.
