New Suspension - Penske 7500 DA

Wow, we're approaching the end of March 2022 already, and my blog posts have certainly been thin on the ground, correction non-existent. The blogs I outlined during the winter of 2021 didn't happen, not through something noteworthy, but just plain old loss of desire to write. Why? My differential replacement project was pretty challenging. Having spent weeks wrestling the differential under the 420R, I didn't have the immediate appetite to blog about my experience. The process was physically and mentally draining, so I took a step back and recharged.

Since the differential replacement project, I've fitted new suspension to the 420R, serviced all the fluids, made further revisions to the cooling system, purchased new wheels and tyres and undertaken my first string alignment. The 420R has received a fair amount of TLC then, I've even found time to start finessing the paint. So there's plenty to blog about. We need to cover a number of product reviews too, from car detailing to a camber gauge. Still I can't believe how the year has flown by!

All of the above will be familiar content for those that follow me on Instagram. If you don't follow me on Instagram, I'd strongly recommend doing so, as all of my Caterham projects and activities are posted there as they happen. The blog often takes a back seat to daily life, and while greater detail will ultimately appear in the blog, Instagram provides that up to date feed. Of course, if you want to ask me anything via Instagram, you're more than welcome!

https://www.instagram.com/caterham7diaries/

Out of the above activities, what shall we cover? I'm going to avoid the differential project for the time being as I need to collate my thoughts into a meaningful post, something that can provide a constructive contribution to the ongoing Titan debate within the Seven community.


Let's discuss the new suspension, a set of Penske 7500 DA with digressive pistons!

Sounds posh!

I'd first like to discuss why I considered and ultimately decided to change my suspension. I wouldn't say there was a single driving reason, more a combination of factors that started the process and ultimately convinced me. The following points aren't in any particular order or priority, merely a reflection of how I recall them.

  • Poor handling during road trips, considering extra weight from luggage and tools, either through a lack of adjustment or operating range.

  • A desire for better handling on bumpy B roads, better composure and confidence in the car. Though it's not bad, I just wanted it to be better.

  • An interest in continuing to develop the car for road use and also testing suspension options to ultimately fit onto the 620R for circuit use.

  • I won't deny, keeping the 'projects' coming, and spannering on the 420R.

Having decided I was serious about swapping my suspension, what came next? Garner some input and expertise from suppliers and experts that know significantly more than me!


I'm sure there are numerous options here with great independent specialists out there, names such as PGM and DPR spring to mind. Given I'd be both installing and configuring the suspension there was only one business I considered, Meteor Motorsport, and Simon Rogers. Before contacting Simon I'd seen plenty of claims made by Simon about his willingness to assist customers pre and post-purchase, further Meteor's product range certainly gave sufficient scope to meet my budget. As I write now, I can confirm Simon has delivered against those claims. He's been incredibly supportive and really helped me understand my suspension options during product selection, and then followed up with the setup support once installed. While I have a basic grasp of suspension setup, I've learnt a lot from Simon. Hats off for customer service!


Having spoken at length with Simon about suspension and the options available I eventually opted for the Penske 7500 DA with digressive fronts. I picked those as I wanted the best 2-way damper without external canisters. I appreciate which 2-way is 'best' is always going to be debatable and with differing views. I suspect at the price point all options will be excellent, having received the Penske and fitted the units, I'm very impressed with the product, and ultimately happy with my personal choice.

My desire to avoid external canisters was not out of fear of use, but space under the 620R engine bay and fitment ease. I intend to use the same suspension on the 620R, assuming I'm satisfied with the performance. Space under the 620R is very limited and so additional canisters is just something I want to avoid. Simon has assured me fitment of canisters on a 620R isn't a problem, which I accepted, but I stuck to my guns.

Penske 7500 DA before fitting
Penske 7500 DA before fitting

Installation of the Penske 7500 DA suspension was simple, and basically a like for like process with the standard suspension. In fact, so similar it embarrassingly caught me out for a moment. The front lower wishbone mount of both the factory-supplied Bilstein and the Penske damper require a collar to be inserted into the lower mount. When removing both front Bilsteins the inserted collar remained in place even though I'd greased it during the original build. As a result, I forgot about it. I then stupidly mounted the new front suspension to the lower wishbone without the collar and immediately spotted a problem. The mount was loose. Having forgotten about the collar, I did start to worry about compatibility issues. I sanity checked the original build from the 'Ikea' manual and my mistake became apparent very quickly. "Doh!" The rest of the installation was a straightforward affair, though I drained the coolant from the 420R (again!) to reach more easily the nearside front top mount. Why? The oil catch-can makes accessing and removing the bolt from the front mount very difficult. Removing the catch-can requires moving the top coolant hose inwards, and that requires draining the coolant. Given this, I took the opportunity to improve the hose, more on that to follow in a forthcoming post.

Once installed the setup work started which really let the quality of the product shine through. All the materials used in the construction are fantastic, the rebound adjuster at the bottom of each strut is a particular highlight consisting of a knurled metal twister which feels great and moves with a satisfying twist and click. They look fantastic too.

Penske 7500 DA Front
Penske 7500 DA Front, fitted to Caterham 7 420R

At the top of each strut, there's a simple hex-head adjuster used to modify compression which moves with an equally satisfying click. The compression adjuster can be reached under the rear arch, but must be orientated facing outwards.

Penske 7500 DA Rear Damper and spring
Penske 7500 DA Rear Damper and spring, Compression adjustment at the top

The ride height platforms are very attractive too and are easy to adjust. Each platform is held in place with two small grub screws that clamp against the damper body. The supplied grub screws have a protector on the end to help reduce damage to the damper body if overtightened. I guess this would be my only criticism, the cost of those grub screws!


https://shop.penskeshocks.com/product/ride-height-set-screw-sc-m6m8-s/


Given the manual states that the screws must not be overtightened yet does not quote a torque value, there's potential for these rather expensive grub screws to come loose through vibration and be lost. The cost might make them rather irritating to replace.


My initial road test with the new suspension fitted wasn't great!


The 420R felt too stiff for a bumpy road, great for circuit use, but not for a bumpy B road. Even though the ride quality wasn't what I was looking for on a B road, over the TT mountain section it felt incredibly composed, a marked improvement. That said, I did find the rear at low speed under tight turns much more lively. It was too easy to break traction at the rear when turning out at a T junction for example. I'd initially set the suspension to what I thought was a middle ground, but clearly my understanding or application was incorrect.


I followed up with Simon, providing my feedback and experience from the first test drive. Simon took the time to point out where I'd gone wrong in my understanding and went on to provide settings aligned with my needs. I've now applied the settings Simon suggested which has transformed the ride and provided exactly what I was looking for. The 420R now drives brilliantly on fast smooth roads and is capable of handling bumpy roads with incredible ease. There is a marked improvement in how the 420R drives at speed, simply put it feels more composed, kind of flat, it's genuinely difficult to describe. It basically feels like a better quality car on the same roads, however, the suspension really shows its value on the bumpy stuff. There is a section of the TT course from Ginger Hall to Ramsey which is notoriously bumpy for cars and bikes. I hate driving it, sadly it's difficult to avoid when driving a lap of the TT course. Each of my previous Lotus Exige Cup cars ran differing versions of Nitrons and they both produced hateful results over that section of road. The standard Bilsteins on the 420R weren't much better either. You either felt you were being bounced around or jarred with a harsh bump, not enjoyable. The improvement from the new Penskes is amazing, yes you can still feel the road is bumpy, but bumps are being managed, softened in a manner I'd not experienced before. The chassis remains composed, there is no jarring movement or uncomfortable bounces. That section of road actually has a 50 mph speed limit, doing more than 50 mph would be quite unpleasant using the standard Bilsteins. Penske 7500 DA can definitely go quicker with comfort, not that I'm promoting it.

All in all, I'm extremely happy and consider the purchase well worth it. Again thank you to Simon at Meteor Motorsport.


The more experienced readers I suspect will be asking what about the spring rates used? I've not mentioned those in the piece as they were selected by Simon based on my input. The spring rates used are 250/130. It's also worth noting my personal experience with Nitrons on a Lotus was particularly poor, however I am aware that Meteor Motorsport brings a lot of value add in terms of tuning and setup of suspension products. I wouldn't consider my experience of Nitrons representative of Nitrons from Meteor Motorsport.

Meteor Motorsport (Race Shocks UK) has a great application for managing suspension setups, known as Circuit Settings. I'll be using the app as I experiment with the setup. If you've got a 2-way suspension setup it's probably worth taking a look.


Circuit Settings App
Circuit Settings App


Weight savings

Individual weights shown.

Rear Bilstein = 3.8kg

Rear Penske 7500 DA = 2.2kg

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