I have found that while all karts respond in the same way when adjusting front ride height, some can be more or less sensitive to that change. I have found that Zanardi karts, as well as most other CRG products may require you to lower the front end as the track grips up, or depending on the tire you’re using. Keep in mind that your Zanardi uses an “offset” spacer system for the front end, so the stock position is actually to have the chassis up (extra spacer on top). Back when we were running Zanardi karts, we would lower the front end in order to reduce responsiveness and shift the balance towards the rear in high speed corners. It’s a good change to experiment with, though you’ll want to make sure you re-align the front end after changing ride height.
I am running an older OTK 2012 Racer. Been fighting a wicked Hop middle out of a tight hairpin at the end of medium straight. Its been suggested by our local OTK Guru to drop the rear to lower COG and maybe a stiffer axle ultimately trying to stiffen the rear to decrease lift. An axle is a big buy for me with no assurance of improvement. My last race, I dropped the rear to lowest setting (highest holes) and left the front centered between the spacers (assuming neutral) . I found myself sitting on the false grid waiting to go out and rolled forward pushing on the front wheels with my feet. I felt the frame protectors at the waist and front scrubbing the ground. It seemed very strange they would be dragging. Felt as the the whole chassis was bowing under my weight (225 lbs). Even the bottom of the seat was only a few millimeters off the ground. I had backed the caster way down and left the camber near 0*. During my first session, the front end felt like it had no grip, but the hop was gone. Between sessions I brought the caster closer to center, but left the camber near 0* (theory if chassis bowing under my weight, then would naturally go negative camber in kart). Front grip improved, but waist was still dragging.
I am a very tall, 6’9" and surprisingly lean for my height. I have found I am quick in the rain, guessing due to weight transfer from my naturally high COG. In the dry, its hard to manage. Seems like the kart wants to twist at the waist excessively. I feel like I loose so much time in that corner, I spend the rest of the track trying to make it up. Fortunately my job in the automotive industry has not affected my work schedule, but with the cancellation of races I have had to time to do some maintenance and upgrades.
I replaced a few worn parts. Got some new frame protectors and started checking ground clearance. Looks like the kart has a natural rake with the front being much lower than the rear. Is this normal for OTK? Not sure if the front of the frame has started to sag. The scraping was enough I decided to raise the rear back to center holes and recheck clearance. Waste was no longer dragging, but front still scrubbed. Next I raised the front, two spacers on top of the spindle arm. Front seems to barely clear. Would this setting yield similar results to only lowering the rear?
Sounds like from this discussion, lower rear is very similar to going to a stiffer axle. I read somewhere that adding rear bar has a similar effect. Stiffening the rear to reduce inside wheel lift. It was used as a litmus test for need of harder axle. Does this sound valid? I feel like there is not much I can do to reduce flex in the waist of the chassis, but between caster reduction and stiffing up the rear I may be able to get a similar result without dragging the pavement. Am I going in the right direction with this?
Sounds like you are testing the right things and thinking in the right direction. It’s entirely possible with a 2012 kart at that weight, that the waist would start to sag a bit. That’s fairly common on older used karts, especially OTK stuff. That being said, typically it doesn’t seem to affect performance, just risks bottoming out and eventually wearing through the rails. The natural rake of the kart is totally normal.
Jacking up the front ride height will actually will increase front grip and the effectiveness of the caster, as it is forcing the inside front down into the corner harder. Lowering front ride height will reduce that effectiveness and essentially desensitize the front end, making the steering lighter.
The rear bar would be my last resort adjustment. It’s really going to negatively affect the kart’s ability to lift the inside rear, and bind the kart up. Before doing that I would go with:
- Negative caster, this isn’t unusual at all for very tall drivers
- Stiffer axle (H or even HH)
- Long rear hubs
Is this a 32mm or 30mm frame? At your height and weight, you really should be on a 32. The 30 is going to have a hard time dealing with the flex your body generates. I know a couple Masters drivers who have tested both back-to-back and on the 30, they reported, “the rear tire felt like it was going to hit me in the head in the corner”.
That is about how it feels. In one of my first races a guy told me it looked like my inside rear was about a foot off the ground. I thought he was exaggerating, but seems now it was not that far from the truth.
I am definitely considering the harder axle, just thought the rear bar could be a confirmation of such. Sounds like you are saying it could make things worse by overshooting my goal? Just wanted to know before dropping another $600 into the old girl.
Since you’re on a budget, before you throw an axle it it I’d consider running the seat below the rails (or move the seat back more) with the front and rear ride height set to stock. What I used to do is sit the frame on some old sprockets and then mount the seat. Then you lower the COG without affecting rake or lowering the entire frame down to the track surface.
Also, have you scaled the kart and looked at the percentages front to rear?
Seat is already below the rails around 6 - 8 mm. I dare not go further without dragging the pavement even at stock ride height. Initially I had the seat further back, hop was worse. I researched the measures again and moved the seat forward then scaled it to verify I was in the correct range. It was like 47/53% +/-1 and side to side weight was within a pound. My seat looks like swiss cheese at this point having played with it so much. At one point the seat was so low, the air compressing under the seat was generating an uncomfortable heat. Not so bad in the winter, but in Texas 100*+ summers it was a bit much…lol!
47% front weight is really high. It’s going to be very difficult to predictably adjust the kart when you’re running that much front weight. You generally want to shoot for 40-44% front, with 44 being a pretty extreme number, and generally taller drivers have less front weight back they can use their body to transfer weight.
I know you said the hopping was worse with it further back, but with that much front I would be pretty worried that tuning adjustments aren’t going to work as they are supposed to. Even if you throw a harder axle in or make the adjustments mentioned before, there’s no guarantee they’ll respond how you want them to.
The rear bar will make the chassis flatter, big time, but it’ll make the whole kart bind.
I’d set the seat back to where it’s supposed to be, go negative on the caster, soften the front bar, make sure the rear width is maxed out, tighten the rear 3rd bearing, and the if you still need more, go with a harder axle.
Just to add to the discussion… some of my thoughts.
My points below are with lowering the rear in mind and what it does.
Vertical Center of Gravity Location:
This does of course change with a ride height change, but keep in mind that the driver is a huge part of the kart weight and center of gravity location. In our example of lowering the rear of the kart, if your seat was already as low as possible at the previous ride height, you now need to raise the seat to give it the required clearance again, taking away a huge chunk of the CG change.
In addition to accounting for the seat, keep in mind that the height of the axle, wheels, tyres, brake disc, hubs, sprocket, carriers, etc. don’t change, so the change in CG isn’t as big as one might suspect at first.
If the main thing you’re going for is a change in vertical center of gravity to increase or slow down how quickly you’re lifting the inside-rear, a change in seat position will accomplish this without creating a change in caster angle.
Of course if the seat did have enough clearance, and you don’t reset it to the same height off the ground… dropping the rear will have a relatively larger effect on handling because of the lower CG.
Front/Rear static weight change:
This is close to zero with ride-height changes. In the example of lowering the rear, it’s easy to think that because the rear is lower, the weight “rolls” down to the rear tyres, but that’s not the case. Going from minimum front and maximum rear height to the opposite, will barely register on the scales.
Caster change:
How much of an effect does a 1 degree change in caster angle have on kart handling?
If I did my drawing/math correct, with a wheelbase of 1050mm, a rear ride height drop of 2cm results in a 1.1 degree increase in positive caster.
I haven’t done the math to compare the relative effects, but I think the change in caster with regards to wheel loading is probably just as big, or greater than the change from center of gravity height - particularly if the seat height is “reset.”
If the seat height isn’t reset after a rear ride-height change, then the magnitude of the effects also depends a lot on driver size/shape/weight. The same ride-height change at a Junior weight level could be fairly different from the same setup change in a “heavy” category. The caster change remains the same, but center of gravity change is different.
In case you haven’t figured out how a change in ride-height changes the caster… it’s much easier to show in a picture than it is to explain in words. Red frame is with the rear ride height lowered, resulting in a 1.1 degree increase in caster.
I vaguely remember someone on the old ekartingnews forums doing the math, and IIRC, the effect of the resultant caster change was more than the ride height change. I don’t recall what he did with regards to the seat position in his calculations.
It’s handy to be aware of this change in caster from ride-height changes. If for example it’s raining and you’re already at maximum caster but still want to do something to raise the inside-rear easier, you might actually be better off lowering the rear ride height to increase caster, and raising the seat to raise the center of gravity.
With front ride height changes, the caster angle of course changes as well (raising front increases caster, lowering it decreases caster). An added complication with the front is that it changes the angle/position of the tie-rods as well - depending on the kart and other steering settings, this can change in different directions. It’s important to reset toe after a front ride-height change, and/or know what the effects are with specific ride height changes.
tl;dr:
- Lowering rear ride height = increasing caster.
- Ride height changes don’t change static loads in any significant amount.
- Lowering rear ride height without “resetting” the seat height = center of gravity change relatively large.
- Lowering rear but setting seat back to the same height = center of gravity change much smaller.
I had never considered the caster change with regards to the ride height change.
Would be interesting to do a back-to-back comparison between a change in ride height vs. a change in seat height to see what difference is felt.
I know that raising the rear ride height dramatically changes the feeling of the kart, so even though it is technically reducing the front caster, it must be a big enough change to overcome that, as I’ve never even noticed a change in how the front feels from a rear ride height change.
Very insightful post Mikko. 
Yeah it’s not easy to separate the two (caster vs CG change). Although they kind of go on opposite directions in setup, it’s not as if they cancel each other out.
For example if there’s enough caster to initially lift the inside rear anyway, a small reduction in caster (0.5-1 degree) from raising the rear won’t stop the jacking effect, and the higher CG will help lift/keep the rear lifted as soon as lateral forces come into play… So the effect also depends on how the kart was handling in the first place.
I suspect (but don’t know and haven’t done the math or tested it) that if countered with a change in seat height, a rear ride height change has very little effect on the center of gravity and thus handling.
On a side note, I run two setups in sim. One with low ride height and raised driver. One with medium ride height and lowered driver. There’s a difference but I can’t articulate it. It’s also a sim so not true to life exactly.
The Racer is a pretty flexible chassis for use in a shifter. I had one, it hopped like mad when the grip came up but during morning practice it was fast. If you can, think about a line that allows power to be applied with the steering relatively straight. Applying power in high grip conditions with the steering wound up causes the chassis to hop.
Lowering the chassis will help. The N axle is too soft for grippy track, an H would be better. There are used out there for a decent price. Also, a kart shop should be able to take the bow out of the center of the frame. Not sure how long that will last but that helps also because the rails are straight and are stiffer.
Thanks, that is on my To Do list as well.
I have to go back and find my notes. I may have transposed the single digits. Weights may be 43/57% instead. I remember going through the seat mounting process several times and then verifying distribution on the scales.
Sounds like in my case, ride height will have less of an effect having to raise the seat. I will continue to play with caster and try to find a harder axle.
Went testing last weekend and I raised the front end to see if I could induce more turn in to reduce a slight push. What was most noticeable was the significantly lower steering effort (I think it helped reduce push, also). Could the slight change in rake make a measurable difference on the steering effort?
Under this notion, you would think raising the front would increase caster and adds to heaviness of steering instead. Were there any other changes made than ride height?
Raising the front end .700, with a 40 inch wheelbase, with 12° caster, increases the caster by 1°. How much did you raise the front end?
If I am not mistaken, narrowing the front track reduces scrub radius and nullifies (if not reverssd the caster change) from dropping the rear height and made the steering feel lighter. Inside front does not drive down as much (i.e less mechanical jacking) and steering feels lighter.
Am I on the right track here Alvin?
@greg, yes narrowing front will reduce steering effort.
@nunley, Probably raise the front around 2 or 3mm.