Wheel Building: Spoke Length Calculation Tools & Tips
Struggling to get spoke length right for your custom wheels? We review the DT Swiss and Prowheelbuilder spoke calculators, and show you how to measure ERD accurately on ultralight carbon rims – helping you succeed on the first try.
When hand-building wheels, few things are more frustrating than miscalculating spoke length – too short and they’re unusable, too long and you have to reorder. This is especially critical when you are using LTC rims, because precision directly affects weight savings and structural integrity.
To help you build more accurately and efficiently, we have put together two spoke calculators that have been proven in countless real world builds. They suit different hub brands. Whether you are a loyal DT Swiss user or prefer other hub brands, you’ll find the right tool here. As LTC, we want you to get it right the first time, so we have also included a practical guide on how to measure ERD on our rims.
1. DT Swiss Spoke Calculator (Recommended for DT Swiss hub users)
If you are using DT Swiss hubs, simply use the official DT Swiss Spoke Calculator. It is optimised for DT Swiss hubs and rims, offers reliable data, and has an intuitive interface – a hassle-free choice for DT users.
👉 Access the DT Swiss Spoke Calculator
2. Prowheelbuilder Spoke Calculator (For other hubs)
If you are using hubs from brands other than DT Swiss, we recommend the Prowheelbuilder Spoke Calculator.
Its biggest advantage is flexibility: you can search for an existing hub model or manually enter your own hub dimensions based on actual measurements.
Why rim ERD is so important – and how to measure ERD on our carbon rims
Choosing the right calculator is only the first step. Accurately measuring the rim’s ERD (Effective Rim Diameter) and hub dimensions is the key to obtaining the correct spoke length. Even a 1 mm error can result in spokes that are too long (dangerous) or too short (unusable).
At LTC, all our rims – whether 38 mm, 50 mm or 60 mm deep – have consistent design ERD values. However, if you are pairing them with specific hubs or lacing patterns, we strongly recommend that you verify the ERD yourself.
How to measure ERD on LTC carbon rims (step-by-step):
On the rim, take two opposite spoke holes and insert a nipple into each.
Insert two old spokes (or smooth metal rods) through the nipples so that they meet inside the rim.
Measure the distance from the end of one spoke to the end of the other spoke, then add the total length of the two spokes that are inside the rim.
Formula: ERD = (Spoke A length + Spoke B length) + length of the gap between them.
Repeat the measurement on 3–4 different pairs of holes and take the average.
Pro tip: Make all measurements to an accuracy of 0.1 mm and double check every input value before using any calculator. A digital caliper is your best friend.
For your convenience, we publish the official ERD data on the specifications (Specs) page of every LTC rim model.
Once you have your hub dimensions (flange diameter, PCD, flange offset, spoke hole diameter) and a verified ERD:
Choose the appropriate calculator based on your hub brand.
Carefully enter all the values.
Cross check the result with the second calculator.
Still unsure about a particular parameter in one of these calculators? Our technical team knows these tools inside and out. We have already helped hundreds of DIY wheel builders avoid expensive rework.
👉 Contact LTC technical support for spoke length advice
Ready to build your dream wheelset?
If you are looking for ultralight, high-performance carbon rims and want spoke calculation to be straightforward, check out our product range:
50 mm aero carbon rims
Every LTC rim comes with documented ERD, clean drilling, and a weight-optimised layup design. Build with confidence – get the right spoke length the first time, with no detours.
Happy building!
