Just finished my 420r build have ride height question

[notoriousjje]

Hello, new here on the forum.  I ordered a 420r January 2024, received it January 2025 and just finished building it.  I wish I had could have gotten it done sooner but kid’s sports got in the way.

 

I took it out for its maiden voyage yesterday and all was good.  I had a question on rideheight.  Does anyone know the recommended height front and rear?  I could not find this information definitively anywhere.  I loved every second of my little 3 mile shake down drive.

 

Thanks in advance!

 

Jero

[MV8]

Looks right to me. Assuming your coilovers are height adjustable, the rear ground clearance to the chassis side rail at the front of the rear tire should be 165-205mm with the front of the rail near a front tire 15mm lower than the rear.

[KnifeySpoony]

Which suspension/dampers/springs do you have? How will you use the car?

 

Setting ride height is a balance between center of gravity height, suspension geometry, suspension travel, ground clearance in order to optimize your desired performance/comfort/practicality. Those factors, dictated by your usage and preferences will determine your optimal ride height. Most people starting with 15mm rake. The lower you go technically the better your mechanical grip. However with a short/long arm suspension you generally don't want to go below parallel with ground on the lower wishbone or handling can suffer because of too-low roll center. With a stiffer spring you can go lower - with a softer spring you need the extra travel in bump to stay off the bump stops. 

[notoriousjje]

10 hours ago, MV8 said:

Looks right to me. Assuming your coilovers are height adjustable, the rear ground clearance to the chassis side rail at the front of the rear tire should be 165-205mm with the front of the rail near a front tire 15mm lower than the rear.

Ok that’s easy enough to measure.  Thanks!

 

Yes I have the threaded Bilsteins.

[notoriousjje]

8 hours ago, KnifeySpoony said:

Which suspension/dampers/springs do you have? How will you use the car?

 

Setting ride height is a balance between center of gravity height, suspension geometry, suspension travel, ground clearance in order to optimize your desired performance/comfort/practicality. Those factors, dictated by your usage and preferences will determine your optimal ride height. Most people starting with 15mm rake. The lower you go technically the better your mechanical grip. However with a short/long arm suspension you generally don't want to go below parallel with ground on the lower wishbone or handling can suffer because of too-low roll center. With a stiffer spring you can go lower - with a softer spring you need the extra travel in bump to stay off the bump stops. 

 

I have the stock Rpack dampers.  They are threaded Bilsteins.  

 

Car is going to be used 20% track 80% weekend fun.

 

Having the front suspension arms level is good advice.  I think I need to raise the car about 1/2 inch.  I’m going to let it all settle and then adjust rideheight and then do a final alignment.

 

Thanks again

[notoriousjje]

[KnifeySpoony]

Yes, would def raise that. On my car (with the "track" dampers, which have significantly higher spring rates than the "sport" setup), I have my front LCA parallel with ground, then the rear about 15mm higher. This does put the bellhousing (lowest point on car) quite low - it will not go over all speed bumps... something to be aware of. 

[notoriousjje]

175mm and 15mm of rake 

[KnifeySpoony]

Where is the 175mm measured?

[notoriousjje]

1 hour ago, KnifeySpoony said:

Where is the 175mm measured?

I was told here chassis rail in front of rear tire.  Then chassis rail in front of front tire 

[KnifeySpoony]

So is 175mm front or rear? 

[MV8]

4 hours ago, KnifeySpoony said:

So is 175mm front or rear? 

Is everything ok? Your questions don't make sense considering all that's been posted.

[notoriousjje]

5 hours ago, KnifeySpoony said:

So is 175mm front or rear? 

175mm to the chassis rail in front of the rear tires.

 

then I measured 160mm to the forward most a arm bolt.  

[JohnCh]

The correct measuring position for the front is the rearward A-am bolt, not the forward bolt. Also, I haven't seen any mention of setting the ride height with fuel and driver's weight in the car. If this was not done, your rear ride heights and rake will be far off. Regarding measured ride heights, keep in mind that people running the 13" wheels will have a different optimal front height due to the smaller tire diameter lowering that number when the A-arm angle is optimal. I have been advised by someone who sets up a lot of Caterhams that he finds a 2 deg downward rake on the lower front A-arm works best. Of course, if that results in too low a ride height for your road conditions, then adjust upwards and maintain that 15mm rake. 

 

From the 2015 build manual, when Caterham still used words rather than oversimplified IKEA diagrams:

 

5.9) Cars fitted with adjustable damper platform

Cars fitted with adjustable damper platforms need to be adjusted to achieve the optimum ride height. This is done by lowering or raising the height of the platforms on the threaded sleeve. It is essential that this task is carried out on level ground.

 

NOTE Lowering the platforms will decrease ride height, and raising the platforms will increase ride height. For the best results the ride height should be set with the driver in the car and fuel in the tank.

 

1. Start by adjusting the front dampers to achieve a minimum distance of 150 mm (this can be increased for road use to a maximum of 190 mm) between the ground and the bottom of the lower chassis rail, where the rear leg of the front lower wishbone exits the side of the car. This measurement should be the same on both sides with the car loaded.

 

2. Now adjust the rear dampers in the same manner to achieve a height 15 mm higher than the front, measured to the underside of the lower chassis rail immediately in front of the 'A' frame mounting point. NOTE Adjusting the rear may have an effect on the front therefore it is good practice to check between front and rear several times during adjustment

 

3. Once the desired ride heights have been set ensure that the platforms are locked together to avoid movement.

 

 

[KnifeySpoony]

Yes, the front should be measured as John mentions, right behind the front LCA on the chassis rail/where the body work wraps around there. I was curious because you have your LCA parallel, but your number seems high. With my LCA parallel, my front ride height is 130mm. Then again I think with the track suspension there are spacers the move spindle position for a lower ride height. But that doesn't account for a 30mm difference. 

[notoriousjje]

This is great info.  I will remeasure and report back.  
 

the front bolt measured 6.75” =171mm

 

[Alex-Ks1]

When I built mine, it finished out at 3 inches ground clearance under the bottom of the trans, it's the lowest area of the car .

I built it the way I wanted it . If I feel there is a bump in the road, I drive over it slow, so far no knocks or bangs .

[MV8]

A 2015 recommendation range might be better than one from the 2014 manual. Both are a long way from 2024 but better than nothing. There is no right or wrong; just preferences. Last owners manual I saw was from 2021 and didn't mention it.

[wdb]

The Lotus Elan folks are pretty big on having the suspension arms parallel to the ground. Using a measure such as suspension arm angle eliminates tire size as a variable. 

[CarlB]

On 12/13/2025 at 10:22 AM, JohnCh said:

The correct measuring position for the front is the rearward A-am bolt, not the forward bolt. Also, I haven't seen any mention of setting the ride height with fuel and driver's weight in the car. If this was not done, your rear ride heights and rake will be far off. Regarding measured ride heights, keep in mind that people running the 13" wheels will have a different optimal front height due to the smaller tire diameter lowering that number when the A-arm angle is optimal. I have been advised by someone who sets up a lot of Caterhams that he finds a 2 deg downward rake on the lower front A-arm works best. Of course, if that results in too low a ride height for your road conditions, then adjust upwards and maintain that 15mm rake. 

 

From the 2015 build manual, when Caterham still used words rather than oversimplified IKEA diagrams:

 

5.9) Cars fitted with adjustable damper platform

Cars fitted with adjustable damper platforms need to be adjusted to achieve the optimum ride height. This is done by lowering or raising the height of the platforms on the threaded sleeve. It is essential that this task is carried out on level ground.

 

NOTE Lowering the platforms will decrease ride height, and raising the platforms will increase ride height. For the best results the ride height should be set with the driver in the car and fuel in the tank.

 

1. Start by adjusting the front dampers to achieve a minimum distance of 150 mm (this can be increased for road use to a maximum of 190 mm) between the ground and the bottom of the lower chassis rail, where the rear leg of the front lower wishbone exits the side of the car. This measurement should be the same on both sides with the car loaded.

 

2. Now adjust the rear dampers in the same manner to achieve a height 15 mm higher than the front, measured to the underside of the lower chassis rail immediately in front of the 'A' frame mounting point. NOTE Adjusting the rear may have an effect on the front therefore it is good practice to check between front and rear several times during adjustment

 

3. Once the desired ride heights have been set ensure that the platforms are locked together to avoid movement.

 

 

Is the 150 MM measurement for the front ride height with Avon 13-inch tires?  I was running my car lower and am having trouble getting the bump steer where I want it. I think it is probably because the instant center is moving around too much. The car has short control arms. 

Edited December 15, 2025 by CarlB