MK Indy Rear Arches Fitting – I Messed Up!

So now I have fitted the front suspension and steering I can now get the wheels on, rear arches on and get the car off the stands and on the ground.

I originally thought that I could leave the chassis on the stands for a while longer and maybe even get the engine in while on the stands. But even though the weight probably wouldn’t be an issue, it would be challenging to get the engine in at that height. It would also have probably made it more difficult to move the car around the garage afterwards. The only reason to keep it up high would be to have easier access for wiring etc. But even for this, it might be more advantageous to have it on the ground. So I decided to move it off the stands once the rear arches were on and put it on wheel dollys instead. So I could still move it around in my single garage more easily.

Wheels & Tyres

I bought my wheels a long time ago. I went for the Team Dynamic Pro Race 1.2 in Anthracite Grey. With a 4×100 PCD 35mm offset and a 15×7 wheel. I now had to get tyres fitted to them.

I ended up going for Toyo Proxes TR1 195/50R15 82V from Protyre which were £63 each. These are road tyres but get very good reviews for both road and occasional track. I wasn’t quite ready to go straight for Toyo R888 semi-slicks at this stage!

We fitted them to the car with the hub-centric rings and new wheel nuts that came with the wheels. I also ensured that the rear flexible brake hoses were fitted with a slight coil, so that they didn’t hit the wheel or the suspension.

MK Indy Rear Arches

We then moved onto the rear arches. This is where I made a BIG mistake! I thought it made sense to leave the car on the chassis stands to fit the arches as it would make access easier. From this perspective, it was the correct move. However, what it meant is that the suspension wasn’t under compression at all, so when lining up the arches with the wheels it didn’t give me the correct picture. You will see the issue later on.

Main Message: Do not fit the rear Arches with the car on stands! Or, if you do have the car on stands, then fully compress the suspension so that the wheel sit exactly in the middle of the arch at the correct height!

For the holes in the arches, I followed the guide which had clear measurements of where to drill the holes.

I also followed the measurements for where the arches should sit on the side panels. I clamped the Arches in the correctly measured position and put the wheel back on. With the wheel hanging down, the alignment looked spot on!

So we continued to drill the holes in the bodywork and fixed the arches with M6 stainless bolts as suggested in the guide. We then used the same approach for the other side. Soon enough both Arches were on and the car was ready to come off the stands. Little did we know at this point that the arches were nowhere near as aligned as they should be!

Removal of the Car from Stands

We then had the challenge of moving the car from the stands to the floor. Fortunately, we had thought of this when designing the stands, they are in two parts. So, the plan was to lift one end with the engine hoist then remove the stand and lower it onto an axle stand. Then do the same at the other end of the car.

So, we moved the car on the stands as far forward in the garage as possible and placed the engine hoist behind the car. We used the same chains for lifting the Mazda MX-5 body from the donor and fixed them to the chassis wrapped in towels to stop any scratches. We removed the rollbar to give better access. The chains were triangulated and we estimated the centre of gravity. As we set up the chains we soon realised that we might be able to lift the whole car from the back in one go.

We started lifting the car off the stands with my Dad in charge of the hoist and my mate Dave and I lifting the front slightly with a bit of support. This worked surprisingly well and we soon had the car on the ground. We put the rear wheels on ramps so we had sufficient clearance underneath to get the engine hoist out once it was down.

A Problem with the MK Indy Rear Arches

Once it was on the ground, we pushed it out the garage to admire our progress and to do the obligatory sit in the car and make engine noises!

It was at this point that we noticed the problem with the rear wheel arches. The wheels were not sitting central in the arch. On the right hand side the arch was actually rubbing on the wheel. I now realised the mistake of fitting the arches without having the car on the ground first. Or at least having the wheel pushed up into the arch area with a jack if the car is on a stand. Let’s just say I was slightly annoyed…

Now, despite me trying to convince myself that something else was wrong, as I had followed the measurements in the manual exactly, I rapidly came to the conclusion that I had simply mounted the arches incorrectly. I did find that the right hand side arch was about 10mm narrower at the opening than the left. I put this down to me storing the bodywork in my shed for 18 months before fitting, which would have gone through at least one hot summer as the panels were still curing.

Fixing the MK Indy Rear Arches

Once the car was back in the garage I then looked at how best to resolve my little issue of the arches not being mounted far enough back.

I worked out I could redrill the holes in the arches themselves and it would shift everything back, this might be enough. I took one side off and clamped it in the ideal position, it might not be quite doable with just moving the holes in the arch. It gave me about 10mm movement before I hit the very edge of the arch with the bolt. I decided it was best to move the holes in the arches as far as I could anyway, it would at least be better than it is right now.

So I redrilled the holes on both sides as close to the edge of the arch as I could. I even used the dremel to carve out a bit of the very inside edge and bent a washer to I could get it further in. I put the arches back on and then used a heat gun on the medium setting to gentle heat up a couple of point of the arch to be more flexible. This allowed it to then sit flat against the bodywork when the bolts were tightened up.



This ended up slightly better but not quite where the perfectionist in me would like. So, I decided to leave it here for the moment and come back to it later on once the car was fully weighted and the suspension was set to the correct height. It will also be easier to do it outside on the drive when the weather is better and where I have more room to be able to see the alignment.

For now it was a great achievement to finally have the car on the ground and a rolling chassis. What a satisfying milestone!

Sold my Euphonic Wheels

I managed to sell my Euphonic wheels on Facebook Marketplace. Sold as seen, needing a full refurbishment and new set of tyres. These are fairly rare in MX5 circles, so I was pleased to get £135 for the set. More money to offset the build cost!

Summary of Build Costs and Hours

Here is a summary of the costs and person hours (total number of hours for every person that has helped) for the build so far. This should hopefully help others with the planning of their builds, by providing cost and time actually incurred for this build. A more detailed breakdown of all the costs and hours worked on the build to date can be viewed here.

Person Hours Worked This Post
Install Wheels and Rear Arches10 hrs
Car Build Costs This Post
4x Toyo Proxes TR1 195/50R15 82V£252
Wheel Dolly's 2nd Hand£60
DONOR PART SOLD - Mazda MX-5 Euphonic Wheels£-135
Totals This Post To Date All Posts
Person Hours Worked 10 hrs 377 hrs 404 hrs
Car Build £177 £12,526 £13,202
Tools / Consumables £0 £459 £470
Total Cost £177 £12,985 £13,672

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